Generative Models

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Generative Models

description

Generative Models. Announcements. Probability Review (Friday, 1:15 Gates B03). Late days…. To be fair…. double late days. Start the p-set early. Where we are. Search. Machine Learning. CS221. Variable Based. Search. Machine Learning. CS221. Variable Based. Search. Machine Learning. - PowerPoint PPT Presentation

Transcript of Generative Models

Page 1: Generative Models

Generative Models

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Announcements

• Probability Review (Friday, 1:15 Gates B03)

• Late days…

• To be fair…

• Start the p-set early

double late days.

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Where we are

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Machine LearningVariable

Based

Search

CS221

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Machine LearningVariable

Based

Search

CS221

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Machine Learning

Search

Variable Based

CS221

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Where We Left Off

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Where We Left Off

Loopy Not loopy

Purple Not Purple Purple Not Purple

Drugged 0.108 0.012 0.072 0.008

Not Drugged 0.016 0.064 0.144 0.576

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Key IdeaIf we have a joint distribution over all variables, then given evidence (which could be multiple variables) E = e, we can find the probability of any query variable X = x.

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These are values in our table!

Y is all variables that aren’t in X or E

Y is all variables that aren’t in E

Key IdeaIf we have a joint distribution over all variables, then given evidence (which could be multiple variables) E = e, we can find the probability of any query variable X = x.

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Key IdeaIf we have a joint distribution over all variables, then given evidence (which could be multiple variables) E = e, we can find the probability of any query variable X = x.

Since we know that p(x | e)’s must sum to 1

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Loopy Not loopy

Purple Not Purple Purple Not Purple

Drugged 0.108 0.012 0.072 0.008

Not Drugged 0.016 0.064 0.144 0.576

Key Idea

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Loopy Not loopy

Purple Not Purple Purple Not Purple

Drugged 0.108 0.012 0.072 0.008

Not Drugged 0.016 0.064 0.144 0.576

Key Idea

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Loopy Not loopy

Purple Not Purple Purple Not Purple

Drugged 0.108 0.012 0.072 0.008

Not Drugged 0.016 0.064 0.144 0.576

Key Idea

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Loopy Not loopy

Purple Not Purple Purple Not Purple

Drugged 0.108 0.012 0.072 0.008

Not Drugged 0.016 0.064 0.144 0.576

Key Idea

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Loopy Not loopy

Purple Not Purple Purple Not Purple

Drugged 0.108 0.012 0.072 0.008

Not Drugged 0.016 0.064 0.144 0.576

Key Idea

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Loopy Not loopy

Purple Not Purple Purple Not Purple

Drugged 0.108 0.012 0.072 0.008

Not Drugged 0.016 0.064 0.144 0.576

Key Idea

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Key Idea

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Our joint gets too big

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Where We Left OffLoopy Not loopy

Purple Not Purple Purple Not Purple

Drugged 0.108 0.012 0.072 0.008

Not Drugged 0.016 0.064 0.144 0.576

Add variable Snowden location: { Hong Kong, Sao Paulo, Moscow, Nairobi, Caracas, Guantanamo}

Size of the table is now 2*2*2*6 = 48

But what does Snowden have to do with drugged out rockstars?

Really are independent…

Joint is exponential in size.

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Independence

l = loopyp = purpled = druggeds = snowden

If we have two tables, one over l, p, d and one for s, we could recreate the joint.

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What else is independent?

SnowdenDrugged

Purple Loopy

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What else is independent?

SnowdenDrugged

Purple Loopy

Purple and loopy?

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What else is independent?

SnowdenDrugged

Purple Loopy

Both caused by drugged

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What else is independent?

SnowdenDrugged

Purple Loopy

If you know drugged, purple and loopy are

independent!

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Conditional Independence

If you know drugged, purple and loopy are

independent!

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If you know drugged, purple and loopy are

independent!

Conditional Independence

Joint

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This is important!

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If you know drugged, purple and loopy are

independent!

𝑃 (𝑙 ,𝑝 ,𝑑)=𝑃 (𝑙 ,𝑝|𝑑 )𝑃 (𝑑)

Conditional Independence

Joint

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If you know drugged, purple and loopy are

independent!

Conditional Independence

Joint

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Drugged

Purple Loopy

No longer need the full joint.

Conditional Independence

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We only need p(var | causes) for each var.

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Model the world with variables

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And what causes what

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Bayesian Network

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Bayesian Network

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Bayesian Network

CoughFeverVomit

FluStomach

Bug

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Bayesian Network

CoughFeverVomit

FluStomach

Bug

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Bayesian Network

Cough (c)Fever (t)Vomit (v)

Flu (f)Stomach bug (s)

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Bayesian Network

Cough (c)Vomit (v)

Flu (f)Stomach bug (s)

Joint

Fever (t)

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Bayesian Network

Joint

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Bayesian Network

Cough (c)Fever (t)Vomit (v)

Flu (f)Stomach bug (s)

Joint

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Definition: Bayes Net = DAGDAG: directed acyclic graph (BN’s structure)

• Nodes: random variables (typically discrete, but methods also exist to handle continuous variables)

• Arcs: indicate probabilistic dependencies between nodes. Go from cause to effect.

• CPDs: conditional probability distribution (BN’s parameters) Conditional probabilities at each node, usually stored as a table (conditional probability table, or CPT)

Root nodes are a special case – no parents, so just use priors in CPD:

iiii xxP of nodesparent all ofset theis where)|(

)()|( so , iiii xPxP

Formally

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What does NSA do with our data?

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Real World Problem

Formal Problem

Solution

Model the problem

Apply an Algorithm

Evaluate

The AI Pipeline

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Live Research

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Research Project

g3

t1 t2 t3

e1 e2 e3

g1 g2 b

i

?

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Research Project

g3

t1 t2 t3

e1 e2 e3

g1 g2 b

i

?

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Research Project

g1 g1*≃?

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Modeling Surprise

g1 g1*≃?

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Competition

Chose top 5

Test how well they predict grades

Select a finalist (gets +)

TA Review

Actually re-grade

Publish?

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On worst pset question

Prize

+Due Tuesday before class (email staff. Subject:

Modeling Regrades)

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Novel Science

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http://vimeo.com/60381274

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What does NSA do with our data?

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Research Project

g3

t1 t2 t3

e1 e2 e3

g1 g2 b

i

?

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Can someone fix this?

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Peer Graders